Two goals of lead (Pb) neurotoxicity research are to identify molecula
r and cellular alterations that underlie behavioral deficits and to de
fine mechanisms of Pb uptake and tolerance in cells that accumulate Pb
. Cell and tissue cultures are practical tools with which to pursue th
ese goals, offering such advantages over in vivo methods as defined ce
ll types, an extracellular environment that can be precisely manipulat
ed, and direct observation. On the other hand, toxicity studies with c
ultured cells also present new challenges of design and interpretation
. If a living vertebrate is like an orchestra playing a Beethoven symp
hony, then tissue culture is like two of the violinists playing their
part alone. Historically, Pb toxicity studies with cell and tissue cul
ture can be divided into an exploratory phase, an expansion phase, and
a newly emerging intensification phase. In the exploratory phase, gro
ss cytotoxic effects from massive Pb exposure (50-500 mu M) were chara
cterized. The collective data suggest differential sensitivity to Pb t
oxicity among various types of cultured neural cells, ranked as follow
s from most to least sensitive: myelinating cells, neurons, and astrog
lia. In addition, astroglia were shown to take up and store large amou
nts of Pb intracellularly, a phenomenon resembling the Pb-sequestering
ability hypothesized for mature astroglia in vivo. The mechanisms of
Pb entry may involve an anion exchanger, Ca2+ channels, or some other
transport process. Three ingrained problems concerning the use of cell
cultures began to emerge: appropriate dose regimens, biologically rel
evant forms of Pb (i.e. ionized or complexed with other molecules), an
d suitable measurements: of Pb effects. These problems received scruti
ny in the expansion phase, during which subcellular targets of Pb-indu
ced damage were examined, specifically membranes, enzymes, and Ca-medi
ated cellular processes. Investigators attempted to define a biologica
lly relevant dose regimen in vitro, as well as a threshold dose below
which Pb had no biological effect Effects of Pb at nanomolar concentra
tions in intact cells and tissue homogenates stimulated the metamorpho
sis of Pb toxicity studies in cell culture into a new phase, the inten
sification phase. Alterations in discrete molecular targets, particula
rly those effects in the cell that may be metabolically amplified, wil
l be a major focus of this phase. Critical molecular targets for Pb-in
duced injury appear to be present during neuritogenesis and/or synapto
genesis. With the availability of cell culture models for neurite exte
nsion and synapse formation, this area may be another focus for innova
tive Pb neurotoxicity research. A third focus should be the concept of
Pb tolerance, particularly in astroglia, which adapt to and tolerate
the presence of intracellular lead. Given the slow turnover of Pb in t
he brain, mechanisms for tolerance are of considerable importance. Unt
il now, little research has been carried out on long-term exposure to
Pb in culture. This issue, above all, requires attention in intensific
ation phase. (C) 1993 Intox Press, Inc.